1. Field of the Invention
The present invention relates generally to an apparatus and method of properly inflating and deflating a surgical balloon and, in particular, to an integrated balloon inflation/deflation device and a method of using the same in a convenient and precise manner without damaging healthy tissue.
2. Description of the Related Art
Surgical balloons are used for procedures such as percutaneous transluminal angioplasty for treatment of stenosis and for occluding blood vessels to prevent release of emboli into the bloodstream during such procedures. During this type of procedure, a guidewire is conventionally used to guide the insertion of the medical instrument, such as a balloon catheter, to the desired treatment site within a patient's vasculature. A hollow guidewire or guidewire catheter with a balloon at its distal tip is often used to anchor the guidewire at the treatment site. A medical instrument such as an occlusion balloon catheter for emboli containment may have multiple lumens and a pair of occlusion balloons. Alternatively, the balloon on the guidewire or catheter may be used for the occlusion of the vessel downstream of the treatment site.
Surgical balloons are typically made of compliant material and increase in diameter with increasing inflation pressure until the balloon burst pressure is reached. Surgical balloons such as occlusion balloons and balloons used for anchoring guidewires must be expanded to contact the blood vessel wall. Clinicians, however, often do not know exactly when the balloon has contacted the blood vessel walls, if uniform circumferential occlusion has been accomplished or whether the balloon has been overinflated.
Conventional surgical balloons are inflated with a syringe coupled to the proximal end of the catheter. The syringe, which is located external to the patient, typically has a fluid capacity of anywhere from 0.5 cc to 10 cc and the clinician uses the syringe to inflate the balloon. The clinician must have considerable patience, skill and concentration to accurately deliver a suitable volume of fluid, such as 0.05 cc, to properly inflate the balloon.
The clinician must also be extremely careful not to overinflate the balloon. Although a pressure gauge is provided on some syringes, the skill required to avoid overinflation is still beyond many clinicians because a very small movement of the syringe piston results in a relatively large injection of fluid. For example, if the clinician desires to deliver about 0.1 cc of fluid to the balloon from a conventional 10 cc syringe, the travel of the syringe piston is less than about 0.7 mm. Thus, it can be readily seen that the control of the syringe to this degree of precision is very difficult. Additionally, unlike therapeutic balloons (which require about 20 atmospheres pressure and can use syringes ranging between about 10 to 20 cc in fluid capacity), typical occlusion balloons require less than about 3 atmospheres pressure and require less than about 1 cc of fluid. Because occlusion balloons are inflated to relatively low pressures with small amounts of fluids, the clinician must be very careful when using a conventional syringe to inflate the balloon.
The risks of imprecision while inflating a surgical balloon with a conventional syringe are substantial. For example, overinflation of the occlusion balloon may cause it to rupture, releasing inflation media into the bloodstream (e.g., fluid, air, gas, etc.), and possibly allowing pieces of the balloon to enter the bloodstream. In addition, the balloon will fail to occlude emboli or anchor the guidewire. Overinflation of the balloon can also damage the healthy tissue adjacent the vessel segment undergoing treatment, even if the balloon does not rupture. The radial expansion of the balloon can also cause undesirable pressure on the vessel wall, and longitudinal expansion of the balloon can create a shearing force which could lead to vessel trauma. Further, if the balloon is overinflated, it may experience a decrease in fatigue strength. For example, if a surgical balloon is overinflated such that it is approximately two to three times its original working length, the balloon may experience a significant decrease in fatigue strength. Underinflation of the balloon also causes many difficulties and problems. An underinflated balloon, for example, may allow fluid to flow around the balloon and the balloon may fail to occlude emboli or anchor the guidewire in the desired position.
Thus, there is a need for a low volume syringe to provide accurate delivery of a suitable amount of fluid to a surgical balloon.
It is also very difficult for the clinician to deliver the desired volume of fluid and then maintain the syringe in a fixed location such that the volume of fluid does not subsequently change. For example, once the clinician has depressed the plunger of the syringe a desired amount to properly inflate the balloon, the clinician must hold the plunger in that position until the pressure equalizes and/or it is desired to deflate the balloon. As discussed above, even small movements of the syringe plunger may cause overinflation or underinflation of the balloon. Thus, the clinician must be very careful not to allow the plunger to move even a very small distance after the fluid is delivered because that may effect the amount of fluid delivered by the syringe.
Thus, a need exists for a syringe which delivers a desired volume of fluid and then does not allow that volume of fluid to be unintentionally changed.
In addition to the problems of overinflation, another problem exists when inflating occlusion balloons. As discussed above, even though the pressure required to inflate the occlusion balloon is generally less than 3 atmospheres, the pressure caused by a conventional inflation syringe causes an immediate build up of pressure near the syringe. The build up of pressure can reach magnitudes of 400 psi. This high pressure caused by conventional syringes often causes leaks in the system and it may damage the balloon. Additionally, this high pressure makes it very difficult for the clinician to properly inflate the balloon to the desired size and pressure.
Thus, there is a need for a syringe that does not create the high build up of pressure created by conventional syringes.